Adult periodontitis is a chronic inflammatory disease involving the supporting structures of the teeth. The interaction between virulence factors of microbial pathogens in dental plaque and the host immune response is a major inducer of the disease. Many inflammatory cytokines have been implicated in the disease process, although direct evidence is presently limited. The lipopolysaccharide (LPS) from gram-negative bacteria may regulate the local inflammatory response in the periodontal pocket and be associated with the chronic nature of the periodontal infection, the gradual destruction of connection tissue, and loss of alveolar bone. Since the gingival crevicular fluid contains products secreted by cells in the gingiva, we developed methods to determine the presence and level of several inflammatory and anti-inflammatory cytokins in samples collected from clinically health and periodontally diseased sites. By Western blot we detected the cytokine proteins tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and transforming growth factor-beta (TGF-beta) at sensitivity levels of 80 ng, 40 ng, and 10 ng, respectively. Our studies involving the collection of inflamed periodontal tissues and examination of cytokine gene expression included amplification of cytokine messenger RNA by the reverse transcriptase-polymerase chain reaction. We identified the presence of the message for cytokines IL-1alpha, l-1beta, TNF-alpha, IL-6, and IL-8 in these tissues. Examination of the in vitro response of mononuclear cells to various LPS preparations was then undertaken, Cultures of the monocytic cell line, U937, were incubated with various amounts of LPS from Porphyromonas or Escherichia coli and proliferation, cell viability, and inflammatory cytokine gene expression were assessed. Our results indicate both concentration and time dependent differences in the effects of the two LPS preparations on the cells.